Pursuant to the provisions of 35 U.S.C. §119(b), this application claims priority to EP11195724.7 filed Dec. 23, 2011, the entire contents of which are incorporated herein by reference.
The present disclosure relates to an n-channel laterally diffused metal-oxide-semiconductor (nLDMOS) device according to the preamble of the first claim.
The integration of high-voltage (HV) and power components into standard logic complementary metal-oxide-semiconductor (CMOS) is one of the most important means of developing cost-effective system-on-a-chip solutions in the field of integrated CMOS-microelectromechanical systems (MEMS), line drivers, universal serial bus interfaces, nonvolatile memory devices, display and light-emitting-diode drivers, 3-D stacked integrated circuits (ICs), automotive, etc.
The HV-tolerant circuit design should be allowed to span the entire design space that the logic design enjoys. However, CMOS technology scaling imposes the reduction of power supply voltage to reduce power consumption and meet the reliability of ultrathin gate oxides (GOXs). As a consequence, reliability constraints such as electrostatic discharges (ESD), electrical overstress across a GOX, and hot-carrier degradation in input/output design can take away the flexibility to cover a broad range of operating voltages. This incompatibility between a technology developed for low-voltage operation and the manufacture of devices in this technology which must be able to withstand higher voltages can be problematic.
The ESD protection of these HV-tolerant devices is very critical. One technique to improve ESD robustness is embedding an additional diffusion region that forms a parasitic silicon-controlled rectifier (SCR) structure with reversible snapback capabilities. This latter device, which is also known as an n-channel LDMOS (nLDMOS)-SCR, is one of the most robust ESD protections since it has excellent clamping capabilities and ESD area performance.
In A. Griffioni et. Al., “OFF-State Degradation of High-Voltage-Tolerant nLDMOS-SCR ESD Devices”, IEEE Transactions On Electron Devices, Vol. 58, No. 7, July 2011, pp. 2061-6071, the OFF-state reliability of HV tolerant nLDMOS-SCR devices is investigated. It was found that the devices suffer from impact ionization induced by electron-conduction-band tunneling from the n+ poly-Si gate to the n-well, which causes degradation of the OFF-state drain current.
It is an aim of the present disclosure to provide an nLDMOS device with improved properties in which OFF-state leakage current from the poly gate to the drain is suppressed.
This aim is achieved according to the disclosure with the nLDMOS device showing the technical characteristics of the first claim.
According to the disclosure, the standard n+ poly gate of prior art nLDMOS devices is replaced by a hybrid n+/p+ poly gate having an n+ part above and extending across the entire channel beyond the nwell/pwell junction and a p+ part above the n-well region.
As a result of the presence of the p+ part, an nLDMOS device with improved properties can be achieved. As will be shown herein, the hybrid n+/p+ poly gate can lead to a suppression of gate leakage currents, enhanced ESD protection and/or enhanced long-term reliability (in high voltage tolerant applications).
An advantage is that the structure according to the disclosure is fully compatible with standard CMOS processes, as the structure is similar to a gated diode structure.
The disclosure will be further elucidated by means of the following description and the appended figures.
The present disclosure will be described with respect to particular embodiments and with reference to certain drawings but the disclosure is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the disclosure.
Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. The terms are interchangeable under appropriate circumstances and the embodiments of the disclosure can operate in other sequences than described or illustrated herein.
Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. The terms so used are interchangeable under appropriate circumstances and the embodiments of the disclosure described herein can operate in other orientations than described or illustrated herein.
The term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It needs to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present disclosure, the only relevant components of the device are A and B.
Nowadays, some applications, such as mixed signal, power and RF functions, are typically realized as stand-alone chips in a mature technology node. The final consumer products are implemented in a System-in-Package (SiP) architecture by assembling several chips in order to achieve a spacey and costly solution. Moreover, to truly benefit from the digital technology advances with the low CMOS cost per area and to further continue portable application miniaturization, these discrete chips are embedded in the multiple functionalities on a single chip using the most advanced digital technology. However, such application implies that the transistors with 1.2 V (or even less) technologies must be able to receive or transmit (to be operated at or sustain) external signal levels up to 3.3 V or 5 V.
The transistors on these transceiving signal paths should thus be able to sustain a higher voltage potential operation, and the corresponding input/output pins also should have dedicated high voltage tolerant ESD protection elements connected to avoid the ESD threats to them. One of the suitable choices is an nLDMOS SCR protection structure. However, prior art devices of this type can be very sensitive to gate leakage and gate oxide degradation in long-term reliability.
The surface part 24 of the n-well region 22 has a length, known in the art as the gate-to-n-well overlap length LGN of 0.1 to 1.0 μm, preferably 0.25 μm. The channel length LCHAN is preferably larger than the LGN.
It is remarked that in reality there is no distinct separation between the regions, as they are defined by doping concentrations which vary gradually in the substrate. For example, the separation line drawn between the p-well and the n-well refers to the fact that on one side (the left hand side on the figure) the p-type doping concentration is higher than the n-type doping concentration and on the other side (the right hand side on the figure) the n-type doping concentration is higher than the p-type doping concentration. This is known in the art and therefore needs no further explanation here. The doping concentrations used in the devices according to the disclosure are standard doping concentrations for CMOS processing (with “+” referring to a higher level doping concentration relative to other regions in the device), so this also needs no further explanation here.
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Number | Date | Country | Kind |
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11195724.7 | Dec 2011 | EP | regional |